The designation "Nippon porcelain" refers to porcelain made in Japan for export to the west, and stamped with the word Nippon on their bases.
U.S. McKinley Tariff Act
This practice began in 1891 in response to the U.S. McKinley Tariff Act, which forbade the import of items that weren't "plainly marked, stamped, branded, or labeled in legible English words."
Nippon vs. Japan or Made in Japan
Nippon (Ni hon = raising sun) is the English spelling of a pronunciation of what Japan is called by the Japanese, but in 1921 "Nippon" was no longer accepted by U.S. Customs Agents as the correct name of origin so from then on, imported Japanese porcelain was supposed to be marked "Japan". It is difficult to tell how well this was followed in practice.
As a dating aid this works out as that any porcelain marked NIPPON is from 1891-1921 and any porcelain marked "Japan" or "Made in Japan" is from after 1921.
However helpful, this rule does not apply to pieces exported to other countries than the US and not even to all of them. This because sometimes paper labels were used and those might well have been washed away of just fallen off.
So, while finding a backstamp saying "Nippon" is a useful dating aid, its absence does not mean that a specific piece of porcelain cannot be from this period.
Today, porcelain that are marked Nippon tends to have a higher value than pieces marked Japan, which unfortunately has created a market for pieces with fake marks.
Japanese potters of this era, studied European porcelain and could successfully imitate the work of for example Limoges, Belleek, and R.S. Prussia.
"Nippon" marked pieces were meant to be sold to the United States, and were hand-painted in an elaborate manner that did not appeal to the Japanese tastes of the day.
The technique was in over glaze enamels, some enhanced with a glass bead surface called coralene.
Most pieces marked "Nippon" were exported out from Japan by the company that later would become Noritake Company even if this was not the only one.
Another technique used in Nippon wares was called moriage, in which strings of clay was applied to a piece like icing on a cake.
A typical example is found in a popular ware that due to the elaborate use of dragons among swirling clouds in raised moriage is called dragon ware. This mostly unmarked ware was made well into the 1950s.
Regarding porcelain marked with Japanese characters Ni or Nichi Hon or Dai Nichi Hon reading Nippon or Dai Nippon (=Japan) written in Japanese kanji characters, this could be found on Japanese porcelain unrelated to customs regulations, clear from the Meiji period (1868-1912) all through the Taisho period (1913-1926) and after what it seems into the 1950s.
Marks where the Dai (great) character is included as in Dai + Nichi + Hon, reading Dai Nippon (= Great Japan), it is generally felt that this on the whole date to the Meiji (1868-1912) period, reflecting the greatly increased nationalism of that period